Eli5: Why are human babies born so ill prepared for the world, compared to some other mammals who are born much more well equipped?
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Because we walk upright, our pelvises can be only so wide. That puts an upper limit to how large-headed babies women can give birth to which is an issue because the defining human trait is our enormous brain.
The compromise is that human babies are born “too early” in order to fit through the birth canal, and then finish their development outside of the womb.
This requires a lot of effort on the parents’ part to keep their offspring alive, but that effort also means that there’s a high chance that any one child makes it to adulthood. Other species (say, salmon) swing the other way and instead pump out a huge amount of offspring with little oversight so that at least some survive.
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